In general, with respect to present air conditioning systems of aircraft, cabin pressurization and cooling is powered by engine bleed pressures at cruise. For example, pressurized air from an engine of the aircraft is provided to a cabin through a series of systems that alter the temperatures and pressures of the pressurized air. To power this preparation of the pressurized air, the only source of energy is the pressure of the air itself. As a result, the present air conditioning systems have always required relatively high pressures at cruise. Unfortunately, in view of an overarching trend in the aerospace industry towards more efficient aircraft, the relatively high pressures provide limited efficiency with respect to engine fuel burn.